For machining operations in metals it is known many different holder assemblies for secure clamping of a cutting tool insert between opposed seating surfaces of clamping jaws or clamping members, which at least to some extent are movable towards and away from each other. The cutting tool inserts are normally made of an expensive and high quality hard metal alloy and therefore it is desirable to make these as small as possible in order to save costs. These conditions puts heavy demands on the holder assemblies to be able to securely clamp the tiny cutting tool inserts to prevent that they will inadvertently be released during the machining operation. Due to the small dimensions of the cutting tool inserts, also the contact surfaces between the clamping members and the cutting tool inserts will be very small. Accordingly, the contact pressure between the clamping members and the cutting tool inserts has to be high to resist the forces, which the inserts will be exposed to during machining. However, the contact pressure is not allowed to be too high since in that case the cutting tool insert might break during clamping or machining operation.
Normally, the clamping pressure between the clamping members is adjusted by means of at least one screw, which is tightened to a certain degree in order to clamp the clamping members towards the cutting tool insert. Accordingly, in order to ensure a sufficient clamping pressure but avoid a too high clamping pressure, which might damage the cutting tool insert, an operator performing a change of cutting tool insert is normally forced to use a torque wrench to ensure correct tightening of the screw. The responsibility for applying the correct clamping force onto the cutting tool insert is accordingly resting on the operator, which gives rise to risks for mistakes. Moreover, releasing and clamping of the cutting tool insert by means of a screw and tightening by means of a torque wrench is time consuming.
From EP 1252954 it is known a cutting tool including a holder assembly in which the clamping mechanism comprises two screws in an angle in relation to each other. One first screw, which functions as a drawbar, is screwed into a first clamping jaw and rests with its head in a seating in a second clamping jaw. The second screw extends in an angle in relation to the first screw and is positioned such that the tip of the second screw meets the head of the first screw. When tightening the second screw it will bear against a conical surface on the head of the first screw such that the first screw will draw the first jaw towards the second jaw when the second screw is tightened as far as it is possible. In this position, the first screw can be used to set the desired clamping force on the cutting tool insert positioned between the first and second clamping jaws. Subsequently, the cutting tool insert can be released by merely loosen the second screw and after exchange of cutting tool insert, the second screw can be tightened as far as it is possible until it is completely stopped against the first screw. In this position the first screw will be automatically drawn to the set position in which the clamping pressure on the cutting tool insert is at the set desirable level without any need for using a torque wrench when tightening. However, this cutting tool suffers from several disadvantages. First of all it is somewhat time consuming to unscrew and tighten the second screw when exchanging the cutting tool insert and after frequently exchanging the cutting tool insert, the tool engagement formations on the second screw may become worn. It is also a risk that the cutting tool insert will not be clamped by the correct clamping pressure since even very small variations of the dimensions of the cutting tool insert will vary the clamping pressure a great deal. Also wear of the contact surfaces between the first and second screws will have a large impact on the clamping force. Furthermore, it is also a possibility that the operator is not careful to draw the second screw until it is completely tightened and stopped against the first screw which will result in an incorrect clamping pressure. The cutting tool as disclosed in EP 1252954 also requires two bores with different orientation, as well as internal threads for each of these bores, which makes the cutting tool expensive and time consuming to produce.